U.S. patent number 5,035,133 [Application Number 07/477,452] was granted by the patent office on 1991-07-30 for method and apparatus for hot die draw forming metal sheets.
This patent grant is currently assigned to Rohr Industries, Inc.. Invention is credited to Thomas J. Liebig, Jeffrey K. Switzer, Robert T. White.
United States Patent |
5,035,133 |
White , et al. |
July 30, 1991 |
Method and apparatus for hot die draw forming metal sheets
Abstract
A method and apparatus for draw forming a metal sheet over a
male form to produce a three-dimensional shape. A sheet of metal is
clamped between upper and lower draw plates positioned above the
male form. The upper plate has an edge conforming to the male form
shape. The plates and sheet are moved downwardly over the form with
the edge of the upper plate firmly pressing the sheet against the
form. The clamping pressure between the draw plates allows suitable
slippage as drawing proceeds to produce a drawn shape of intended
thickness. The drawn shape has a configuration conforming to the
outer surface of the male form and has an outer surface of improved
uniformity and appearance due to the wiping action of the upper
plate edge.
Inventors: |
White; Robert T. (Spring
Valley, CA), Liebig; Thomas J. (Chula Vista, CA),
Switzer; Jeffrey K. (Poway, CA) |
Assignee: |
Rohr Industries, Inc. (Chula
Vista, CA)
|
Family
ID: |
23895970 |
Appl.
No.: |
07/477,452 |
Filed: |
February 9, 1990 |
Current U.S.
Class: |
72/350;
72/296 |
Current CPC
Class: |
B21D
25/02 (20130101) |
Current International
Class: |
B21D
25/00 (20060101); B21D 25/02 (20060101); B21D
024/08 () |
Field of
Search: |
;72/296,297,309,350,351,400,401,381,57 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Larson; Lowell A.
Assistant Examiner: McKeon; M. J.
Attorney, Agent or Firm: Schlesinger; Patrick J. Gilliam;
Frank D.
Claims
We claim:
1. The method of drawing forming sheet metal into a product having
a complex shape which comprises the steps of:
providing a male form conforming to the interior shape of the
product;
providing upper and lower draw plates having relative movement
therebetween, said upper plates each having an edge conforming to a
corresponding surface of said male form and an elongated upstanding
bead on the upper surface of said lower plate and a corresponding
groove on the lower surface of said upper plate, said groove in
said lower surface having sufficient width to accommodate relative
movement between the bead and groove surfaces during drawing;
clamping a sheet of metal between said upper and lower plates, said
bead and groove adapted to press said sheet therebetween during
drawing;
heating said sheet and said male form to a selected elevated
temperature; and
drawing said sheet of metal downwardly, transverse to said relative
movement of said upper and lower draw plates, over said male form
with said upper plate edge pressing said metal sheet firmly against
said male mold;
the clamping pressure between said upper and lower plates selected
to allow said sheet to slip from between said plates as drawing
progresses.
2. The method according to claim 1 wherein said edge is pressed
against said sheet during drawing with a pressure in the range of 0
to 500 psi.
3. The method according to claim 2 wherein said edge is rounded to
provide a wiping and coining action on the exterior surface of said
metal sheet during drawing.
4. The method according to claim 1 wherein said metal comprises
aluminum and said sheet and said form are heated to a temperature
in the range of 300.degree. to 500.degree. F.
5. The method according to claim 1 wherein said upper and lower
plates are clamped together at a pressure in the range of 40 to 120
psi during draw.
6. Apparatus for draw forming sheet metal over a male form to
produce a product having a complex shape which comprises:
a male form having an exterior shape corresponding to the interior
shape of the product;
upper and lower draw plates positioned adjacent to said male form
and adapted to clamp a sheet of metal therebetween, an elongated
upstanding bead on the upper surface of said lower plate and a
corresponding groove on the lower surface of said upper plate, said
groove in said lower surface having sufficient width to accommodate
relative movement between the surfaces during drawing, said bead
and groove adapted to press said sheet therebetween during
drawing;
heating means for heating said form and a metal sheet clamped
between said plates to a selected temperature;
said upper plate having edges corresponding to the shape of said
metal form;
means for moving the assembly of sheet and plates downwardly,
transverse to the relative movement of said upper and lower draw
plates, over said form with said sheet in contact with said form;
and
means for firmly pressing said edges of said upper plate toward
said form.
7. The apparatus according to claim 6 wherein said edge is rounded
to cause a wiping and coining action on a metal sheet as said edge
is moved along a metal sheet on said form.
8. The apparatus according to claim 6 wherein said means for
pressing said edge toward said form is adapted to produce pressure
in the range of 0 to 500 psi.
Description
cl BACKGROUND OF THE INVENTION
This invention relates in general to the draw forming of metal
sheets and, more specifically, to a method and apparatus for deep
draw forming complex shapes.
A wide variety of methods and apparatus have been developed of
forming metal sheets into three-dimensional products. These methods
and apparatus are of varying effectiveness, depending on the shape
to be produced and physical characteristics required in the
product.
Stretch forming, in which opposite edges of a large metal sheet are
clamped with a plurality of clamps and the sheet is stretched over
a three-dimensional form, is widely used for large panels such as
aircraft fuselage skins. Typical of these methods is that disclosed
by Gray in U.S. Pat. No. 3,299,688. While very useful with large
panels with minor reshaping, this method is difficult to apply to
more significant reshaping of smaller panels.
Aluminum beverage cans and similar shapes are often formed from
sheet material by a punch moving through an opening in a circular
clamping mechanism which holds the sheet, such as is described by
Clowes in U.S. Pat. No. 3,789,649. While effective for small parts,
it has proven difficult to apply the punch techniques to large
parts, where wrinkles, orange peel and grain growth may occur,
reducing panel strength and producing a poor cosmetic
appearance.
Other methods have been used for forming large shapes from sheet
material, such as drop hammer forming, cold drawing, hydro bulge
forming, etc. These methods tend to require several forming steps,
with intermediate heat treating, to prevent excessive grain growth
and often require considerable hand work on the product for
cosmetic reasons. Spin forming is useful in some cases, but is
limited to round or near-round shapes. Super plastic forming has
advantages, but tends to be complex and expensive, be limited in
suitable alloys and the product requires considerable surface
cleanup.
Thus, there is a continuing need for an improved method and
apparatus for forming three-dimensional shapes from sheet metal
which is simple, economical and produces a product having a surface
requiring little, if any, hand finishing.
SUMMARY OF THE INVENTION
The above-noted problems, and others, are overcome in accordance
with this invention, fundamentally, by a method and apparatus in
which a sheet of metal is clamped between upper and lower draw
plates adjacent to a male form, the clamped sheet is drawn down
over the male form with a rounded edge of the upper plate firmly
pressing the sheet against the male form. Upon completion of draw
plate movement, a three-dimensional product having a configuration
conforming to that of the male form results. The product has a very
high quality exterior surface, apparently due to the wiping/coining
action of the upper plate edge.
The male form includes internal heating devices to maintain the
form at a desired elevated temperature. The entire apparatus is
located within an enclosure and maintained at a suitable elevated
temperature. Typically, these temperatures may be about 300.degree.
F. for aluminum 2219 alloy.
BRIEF DESCRIPTION OF THE DRAWING
Details of the invention, and of a preferred embodiment thereof,
will be further understood upon reference to the drawing,
wherein:
FIG. 1 is a schematic plan view of the apparatus of this
invention;
FIG. 2 is a schematic section view taken on line 2--2 in FIG. 1 at
the beginning of the drawing operation; and
FIG. 3 is a schematic section view taken on line 2--2 in FIG. 1 at
completion of the drawing operation.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Considering FIGS. 1 and 2 together, there is seen hot drawing
assembly 10 at the beginning of the drawing operation. In this
embodiment, a segment of a generally circular inlet lip for a jet
engine nacelle is to be formed.
A sheet of metal 12 to be reshaped is clamped between upper draw
plate 14 and lower draw plate 16. Plates 14 and 16 are supported by
a large conventional hydraulic press (not shown) which moves the
plate assemblies downwardly, as indicated by arrows 18.
A male form 20 rest on a base plate 22. Form 20 may be made from
any suitable material, such as Kirksite. A plurality of electrical
heaters 24 are embedded within form 20. Thermocouples 26 are also
embedded in form 20 to continuously measure internal
temperature.
The entire assembly 10 is contained within an enclosure. The
temperature of the enclosure and form 20 is regulated by a
conventional heater controller, not shown. For aluminum alloys,
male form 20 and the sheet to be formed should be maintained at a
temperature of from about 300.degree. to 500.degree. F.
A bead 28 secured to the upper surface of lower plate 16 forces
metal sheet 12 slightly upwardly into a wide groove 30 in the lower
surface of upper clamp plate 14.
Bead 28 clamps metal sheet against the inner wall of groove 30 to
produce uniform clamping pressure around the forming region and to
permit slippage at the desired rate during forming.
Prior to the forming operation, metal sheet 12 is held flat between
draw plates 14 and 16 above form 20 as the plate assembly is
lowered, metal sheet 12 engages and begins to conform to form 20.
Upper draw plates 14 are pressed toward form 20, firmly pressing
sheet 12 thereagainst. The engaging edge 32 is curved to provide a
wiping or coining action which smoothes the surface of metal sheet
12 reducing or eliminating surface defects.
Edge 32 is pressed against sheet 12 with any suitable pressure, as
schematically indicated by springs 34. Typically, this pressure may
be in the 0 to 500 psi range with aluminum alloys such as 2219.
Conventional empirical tests will be used to select optimum edge
pressures for other alloys.
As the plate assembly moves downwardly to the final position shown
in FIG. 3, metal sheet 12 slides out from between clamp plates 14
an 16 onto the surface of form 20. As form 20 widens, upper plate
14 moves outwardly relative to lower plate 16, with groove 30
moving outwardly but still accommodating bead 28. The pressure
between draw plates 14 and 16 need only be sufficient to permit
smooth feeding of metal sheet 12 past edge 32, typically in the 40
to 120 psi range.
While certain specific configurations and arrangements were
described in the above description of a preferred embodiment, those
can be varied, where suitable, with similar results. Other
applications and variations of this invention will occur to those
skilled in the art. Those are intended to be included within the
scope of this invention as defined in the appended claims.
* * * * *